1. Field of the Invention
The present invention relates generally to a method and system for initiating a Push to Talk (PTT) over Cellular (PoC) session between PoC clients supporting various types of media, and more particularly to a method and system for enabling a session to be independently and simply initiated between a Controlling PoC server (CF) and a transmitting party PoC client regardless of answer modes set according to the media types, when a session participating PoC client sets different answer modes depending on the media types on a receiving party Participating PoC server (PF) in a multimedia PoC environment.
2. Description of the Related Art
Significant development of mobile communication technologies and expansion of communication networks have enabled wide-ranging services and applications using mobile phones. Diversification of user requests causes the services to be expanded to a positioning, a multimedia and a Push to Talk (PTT) service without being limited to a simple communication service. Particularly, the PTT service supports not only a group and a voice communication which have been available in a conventional radio transmitter and a Trunked Radio System (TRS), but also various additional functions such as an instant messenger and a status display.
Currently, extensive research is being performed so as to standardize a PoC service which employs such a PTT concept in a mobile communication network. One of the features of the PoC service that distinguishes it from the conventional mobile communication service, is that a user can make a call while moving between sessions if necessary, because he/she belongs to a plurality of sessions. The requirement that a user be able to communicate while moving among a plurality of sessions, that is, the requirement for a multi-session function is specified in the Open Mobile Alliance (OMA), which is a body defining the mobile communication services.
The PoC V2.0 system supports a PoC multimedia communication service and defines new types of multimedia such as video, image and text. Further, current PoC systems can display multi-streams such as a video or image due to the improved performance of terminals.
Then, the flow of signals when an auto-answer mode has been set between a receiving party PoC client and a PoC server during a PoC session initiation procedure in the PoC system including the PoC client supporting various types of media, as mentioned above, will be described with reference to FIG. 4.
As illustrated in FIG. 4, receiving party PoC client B sets a answer mode for receiving media on PoC server B through PoC service setting at step 400. The answer mode includes an auto-answer mode and a manual-answer mode. Since only voice has been supported by PoC V1, the user was able to set the auto-answer mode for voice. Here, if the PoC client B sets the auto-answer mode for voice at step 400, the PoC server B transmits an acknowledgement message at step 402, thereby completing an answer mode setting for media to be received by the PoC client B.
When PoC client A, which desires to establish a PoC session, transmits a session participation request message (i.e., an INVITE message) to PoC server A including a PF and a CF at step 404, the CF forwards the session participation request message to the PoC client B, which has been invited, through the PoC server B at steps 406 and 412. Before forwarding the session participation request message to the PoC client B, the PoC server B identifies that the answer mode of the PoC client B has been set to an auto-answer mode through the PoC service setting established in steps 400 and 402, and transmits an automatic response message to the session participation request message to the CF at step 408. After receiving the automatic response message, the CF transmits an unconfirmed OK response to the PoC client A at step 410 so as to initiate a PoC session in advance before receiving the final OK response of the PoC client B. When an automatic response PoC session is initiated through the procedure, the CF gives a Talk Burst Granted floor to the PoC client A at step 414, and the PoC client A starts media transmission at step 416.
After buffering media received from the PoC client A, the CF transmits the buffered media to the PoC client B through steps 424 and 426 when receiving the final OK response of the PoC client B to the session participation request message (i.e., INVITE message) at step 420 and step 422.
As described above, when a session is initiated based on the conventional PoC V1, types of transmittable media are limited to voice or PoC speech, so that it is possible to establish the corresponding PoC session through the answer mode setting. However, according to PoC 2.0, various types of video, images and texts can be transmitted in addition to voice. Therefore, upon establishing a PoC session supporting various PoC multimedia services, as described above, if the answer modes according to media types are not equal to each other, the PoC server cannot decide what answer mode the PoC server will follow in performing the response, thereby causing an error.
That is, since the PoC V2.0 system does not support answer modes for various types of media, there may be a limitation in session establishment when the answer modes according to various media types supported by the PoC V2.0 are not equal to each other.